Programmable metallization memory cell with planarized silver electrode

ABSTRACT

Programmable metallization memory cells having a planarized silver electrode and methods of forming the same are disclosed. The programmable metallization memory cells include a first metal contact and a second metal contact, an ion conductor solid electrolyte material is between the first metal contact and the second metal contact, and either a silver alloy doping electrode separates the ion conductor solid electrolyte material from the first metal contact or the second metal contact, or a silver doping electrode separates the ion conductor solid electrolyte material from the first metal contact. The silver electrode includes a silver layer and a metal seed layer separating the silver layer from the first metal contact.

BACKGROUND

Memory devices are common in electronic systems and computers to storedata. These memory devices may be volatile memory, where the stored datais lost if the power source is disconnected or removed, or non-volatile,where the stored data is retained even during power interruption. Anexample of a non-volatile memory device is the programmablemetallization cell (PMC) that is also known as a conductive bridging RAM(CBRAM), nanobridge memory, or electrolyte memory.

A PMC utilizes an ion conductor such as a chalcogenide type or an oxidetype and at least two electrodes (e.g., an anode and a cathode) with theion conductor between the electrodes. When a voltage is applied acrossthe electrodes, superionic clusters or conducting filaments rapidly growfrom the cathode through the ion conductor towards the anode. This givesrise to a low resistance state. When an electric field of oppositepolarity is applied across the electrodes, the conducting filamentsdissolve and the conducing paths are disrupted. This gives rise to thehigh resistance state. The two resistance states that are switchable bythe application of the appropriate electric field are used to store thememory data bit of “1” or “0”.

An exemplary PMC utilizes germanium selenide with silver ions diffusedtherein. Current methods provide silver ions within the germaniumselenide material by initially depositing the germanium selenide glasslayer onto a substrate, typically a first electrode, and then depositinga thin overlying layer of silver, typically by physical vapor deposition(i.e., sputtering). The thin silver layer can then exposed toelectromagnetic energy such as ultraviolet (UV) radiation to diffusesilver into the germanium selenide layer, such that a homogenousdistribution of silver throughout the layer is ultimately achieved. Theupper electrode can then be formed from silver that is sputter depositedonto the metal-doped germanium selenide layer.

However, the formation of the silver electrode is wrought withdrawbacks. For example, issues of adhesion, agglomeration andnon-uniform thickness plague the formation of the silver electrode forthe PMC. Therefore, a need exists for a PMC construction and processesfor fabricating PMC that avoids such problems.

BRIEF SUMMARY

The present disclosure relates to programmable metallization memorycells having a planarized silver electrode and methods of forming thesame are disclosed.

In one illustrative embodiment the programmable metallization memorycell include a first metal contact and a second metal contact. An ionconductor solid electrolyte material is between the first metal contactand the second metal contact. A silver alloy doping electrode separatesthe ion conductor solid electrolyte material from the first metalcontact or the second metal contact. The silver alloy electrode includesan atomic mixture of silver atoms and aluminum atoms, copper atoms, goldatoms, ruthenium atoms, or titanium atoms.

In another illustrative embodiment a programmable metallization memorycell includes a first metal contact and a second metal contact. An ionconductor solid electrolyte material is between the first metal contactand the second metal contact. A silver doping electrode separates theion conductor solid electrolyte material from the first metal contact.The silver doping electrode includes a silver layer and a metal seedlayer separating the silver layer from the first metal contact.

One illustrative method of forming a programmable metallization memorycell includes disposing an ion conductor solid electrolyte materialbetween a first metal contact and a second metal contact and depositinga silver doping electrode between the ion conductor solid electrolytematerial and the first metal contact or the second metal contact. Thedepositing step forms a silver doping electrode having a surface RMSroughness of less than 2.0 nm.

These and various other features and advantages will be apparent from areading of the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure may be more completely understood in consideration of thefollowing detailed description of various embodiments of the disclosurein connection with the accompanying drawings, in which:

FIG. 1 is a schematic diagram of an illustrative programmablemetallization memory cell in a low resistance state;

FIG. 2 is schematic diagram of an illustrative programmablemetallization memory cell in a high resistance state;

FIG. 3 is a schematic diagram of an illustrative programmablemetallization memory unit including a semiconductor transistor;

FIG. 4 is a schematic diagram of an illustrative programmablemetallization memory array;

FIG. 5 is a schematic diagram of an illustrative programmablemetallization memory cell having a metal seed layer and a silver layerforming a silver doping electrode;

FIG. 6 is a schematic diagram of an illustrative programmablemetallization memory cell having a lower silver alloy doping electrode;

FIG. 7 is a is a schematic diagram of an illustrative programmablemetallization memory cell having an upper silver alloy doping electrode;and

FIG. 8 is a flow diagram of an illustrative method of forming aprogrammable metallization memory cell.

The figures are not necessarily to scale. Like numbers used in thefigures refer to like components. However, it will be understood thatthe use of a number to refer to a component in a given figure is notintended to limit the component in another figure labeled with the samenumber.

DETAILED DESCRIPTION

In the following description, reference is made to the accompanying setof drawings that form a part hereof and in which are shown by way ofillustration several specific embodiments. It is to be understood thatother embodiments are contemplated and may be made without departingfrom the scope or spirit of the present disclosure. The followingdetailed description, therefore, is not to be taken in a limiting sense.The definitions provided herein are to facilitate understanding ofcertain terms used frequently herein and are not meant to limit thescope of the present disclosure.

Unless otherwise indicated, all numbers expressing feature sizes,amounts, and physical properties used in the specification and claimsare to be understood as being modified in all instances by the term“about.” Accordingly, unless indicated to the contrary, the numericalparameters set forth in the foregoing specification and attached claimsare approximations that can vary depending upon the desired propertiessought to be obtained by those skilled in the art utilizing theteachings disclosed herein.

The recitation of numerical ranges by endpoints includes all numberssubsumed within that range (e.g. 1 to 5 includes 1, 1.5, 2, 2.75, 3,3.80, 4, and 5) and any range within that range.

As used in this specification and the appended claims, the singularforms “a”, “an”, and “the” encompass embodiments having pluralreferents, unless the content clearly dictates otherwise. As used inthis specification and the appended claims, the term “or” is generallyemployed in its sense including “and/or” unless the content clearlydictates otherwise.

Spatially related terms, including but not limited to, “lower”, “upper”,“beneath”, “below”, “above”, and “on top”, if used herein, are utilizedfor ease of description to describe spatial relationships of anelement(s) to another. Such spatially related terms encompass differentorientations of the device in use or operation in addition to theparticular orientations depicted in the figures and described herein.For example, if a cell depicted in the figures is turned over or flippedover, portions previously described as below or beneath other elementswould then be above those other elements.

As used herein, when an element, component or layer for example isdescribed as being “on” “connected to”, “coupled with” or “in contactwith” another element, component or layer, it can be directly on,directly connected to, directly coupled with, in direct contact with, orintervening elements, components or layers may be on, connected, coupledor in contact with the particular element, component or layer, forexample. When an element, component or layer for example is referred toas begin “directly on”, “directly connected to”, “directly coupledwith”, or “directly in contact with” another element, there are nointervening elements, components or layers for example.

The present disclosure relates to programmable metallization memorycells having a planarized silver electrode and methods of forming thesame are disclosed. A silver electrode in the programmable metallizationmemory cell can be formed of a silver alloy or be formed of a bi-layerof a metal seed layer and a silver layer. These silver electrodes have asurface RMS roughness of less than 2.0 nm and enable the integrationcompatibility and improve the uniformity of the programmablemetallization memory cell. While the present disclosure is not solimited, an appreciation of various aspects of the disclosure will begained through a discussion of the examples provided below.

FIG. 1 is a schematic diagram of an illustrative programmablemetallization memory cell 10 in a low resistance state. Programmablemetallization cell (PMC) memory is based on the physical re-location ofsuperionic regions within an ion conductor solid electrolyte material16. The PMC memory cell 10 includes an electrochemically active dopingelectrode 18, an ion conductor solid electrolyte material 16, a firstmetal contact 12, and a second metal contact 14. The ion conductor solidelectrolyte material 16 is between the first metal contact 12 and thesecond metal contact 14. The doping electrode 18 separates the ionconductor solid electrolyte material 16 from the second metal contact14.

The doping electrode 18 described herein can be formed of a silver alloyor formed of a bi-layer of a metal seed layer and a silver layer. Thesilver doping electrodes described herein provide a planarized silverelectrode, that is, the silver doping electrode has a surface RMSroughness of less than 2.0 nm, at a deposition thickness of 60 nm asdescribed below. A pure silver doping electrode deposited as describedherein has been shown to have a surface RMS roughness of greater than 10nm, at a deposition thickness of 60 nm, rendering the silver dopingelectrode too rough for most integration compatibility without anadditional planarization step such as, for example, CMP. This planarizedsilver doping electrode allows the silver doping electrode to bedeposited on or adjacent to a semiconductor substrate utilizingsemiconductor fabrication techniques and then the ion conductor solidelectrolyte material can be deposited on the silver doping electrode andstill provide a relatively uniform layer formation of the ion conductorsolid electrolyte material without the need for an additionalplanarization step such as, for example, CMP.

The first metal contact 12 and the second metal contact 14 can be formedof any useful metallic material. In many embodiments, one or both of thefirst metal contact 12 and a second metal contact 14 are formed ofelectrochemically inert metals such as, for example, platinum, gold, andthe like. In some embodiments the first metal contact 12 and/or a secondmetal contact 14 have a two or more metal layers, where the metal layerclosest to the ion conductor solid electrolyte material 16 iselectrochemically inert while additional layers can be electrochemicallyactive.

The ion conductor solid electrolyte material 16 can be formed of anyuseful material that provides for the formation of conducting filaments17 within the ion conductor solid electrolyte material and extendbetween the doping electrode 18 and the metal contact 12 uponapplication of an electric field EF+. In many embodiments the ionconductor solid electrolyte material 16 is a chalcogenide-type materialsuch as, for example, GeS₂, GeSe₂, CuS₂, CuTe, and the like. In otherembodiments the ion conductor solid electrolyte material 16 is anoxide-type material such as, for example, WO₃, SiO₂, Gd₂O₃ and the like.

Application of an electric field EF+ across the doping electrode 18 andthe metal contact 12 allow doped cations (i.e., silver ions) to migratefrom the doping electrode 18 toward the metal contact 12, formingconducting filaments 17 within the ion conductor solid electrolytematerial 16. The presence of the conducting filaments 17 within the ionconductor solid electrolyte material 16 reduces electrical resistancebetween the first metal contact 12 and the second metal contact 14 andgives rise to the low resistance state of the programmable metallizationmemory cell 10.

Reading the PMC 10 simply requires a small voltage applied across thecell. If the conducting filaments 17 are present in that cell, theresistance will be low, leading to higher current, which can be read asa “1”. If there are no conducting filaments 17 present, the resistanceis higher, leading to low current, which can be read as a “0” asillustrated in FIG. 2.

FIG. 2 is schematic diagram of an illustrative programmablemetallization memory cell 10 in a high resistance state. Application ofan electric field of opposite polarity FE− ionizes the conductingfilaments and moves the doping ions back to the doping electrode 18 andgives rise to the high resistance state of the programmablemetallization memory cell 10. The low resistance state and the highresistance state are switchable with an applied electric field and areused to store the memory bit “1” and “0”.

FIG. 3 is a schematic diagram of an illustrative programmablemetallization memory unit 20 including a semiconductor transistor 21.The programmable metallization memory unit 20 includes a programmablemetallization memory cell 10, as described herein electrically coupledto a semiconductor transistor 22 via an electrically conducting element24. The semiconductor transistor 22 includes a semiconductor substrate21 having doped regions (e.g., illustrated as n-doped regions) and achannel region (e.g., illustrated as a p-doped channel region) betweenthe doped regions The transistor 22 includes a gate 26 that iselectrically coupled to a word line WL to allow selection and current toflow from the bit line BL to the second metal contact 28. An array ofprogrammable metallization memory unit 20 can be formed on asemiconductor substrate utilizing semiconductor fabrication techniques.

FIG. 4 is a schematic diagram of an illustrative programmablemetallization memory array 30. The programmable metallization memoryarray 30 includes a plurality of word lines WL and a plurality of bitlines BL forming a cross-point array. At each cross-point a programmablemetallization memory cell 10 is electrically coupled to a word line WLand a bit line BL. A select device (not shown) can be at eachcross-point or at each word line WL and bit line BL.

FIG. 5 is a schematic diagram of an illustrative programmablemetallization memory cell 30 having a metal seed layer 35 and a silverlayer 38 forming a silver doping electrode. The programmablemetallization memory cell 30 includes a first metal contact 36 and asecond metal contact 34. The first metal contact 36 is deposited on oradjacent to a semiconductor substrate 31, thus the first metal contact36 can also be referred to as the lower metal contact 36 or bottom metalcontact 36. The second metal contact 34 is deposited after the firstmetal contact 36. The second metal contact 34 can also be referred to asthe upper metal contact 34 or top metal contact 34.

An ion conductor solid electrolyte material 32 (described above) isbetween the first metal contact 36 and the second metal contact 34. Asilver doping electrode separates the ion conductor solid electrolytematerial 32 from the first metal contact 36. The silver doping electrodeincludes a silver layer 38 and a metal seed layer 35 separating thesilver layer 38 from the first metal contact 36.

The metal seed layer 35 can be formed of any useful metal and have anyuseful thickness. In many embodiments the metal seed layer 35 is formedof titanium, aluminum, or ruthenium. In many embodiments the metal seedlayer 35 has a thickness in a range from 0.3 to 20 nm or from 0.5 to 5nm. The metal seed layer 35 can be deposited utilizing any useful methodsuch as, for example, physical vapor deposition techniques.

The silver layer 38 can have any useful thickness. In many embodimentsthe silver layer 38 has a thickness in a range from 5 to 200 nm or from10 to 100 nm. The silver layer 38 can be deposited utilizing any usefulmethod such as, for example, physical vapor deposition techniques. Inmany embodiments the silver layer 38 has planarized or smooth surface,e.g., a surface RMS roughness of less than 2.0 nm.

FIG. 6 is a schematic diagram of an illustrative programmablemetallization memory cell 40 having a lower silver alloy dopingelectrode 45. The programmable metallization memory cell 40 includes afirst metal contact 46 and a second metal contact 44. The first metalcontact 46 is deposited on or adjacent to a semiconductor substrate 41,thus the first metal contact 46 can also be referred to as the lowermetal contact 46 or bottom metal contact 46. The second metal contact 44is deposited after the first metal contact 46. The second metal contact44 can also be referred to as the upper metal contact 44 or top metalcontact 44.

An ion conductor solid electrolyte material 42 (described above) isbetween the first metal contact 46 and the second metal contact 44. Asilver alloy doping electrode 45 separates the ion conductor solidelectrolyte material 42 from the first metal contact 46. The silveralloy doping electrode 45 includes an atomic mixture of silver atoms andaluminum atoms, copper atoms, gold atoms, ruthenium atoms, or titaniumatoms. In some embodiments the silver alloy doping electrode 45 includesan atomic mixture of silver atoms and aluminum atoms. In someembodiments the silver alloy doping electrode 45 includes an atomicmixture of silver atoms and copper atoms. In some embodiments the silveralloy doping electrode 45 includes an atomic mixture of silver atoms andtitanium atoms. The silver alloy can be formed of any useful amount ofsilver and other metal as described above. In many embodiments thesilver alloy includes from 50 to 85% atomic % sliver and from 50 to 15atomic % of aluminum atoms, copper atoms, gold atoms, ruthenium atoms,or titanium atoms. The silver alloy doping electrode 45 can have anyuseful thickness. In many embodiments the silver alloy doping electrode45 has a thickness in a range from 5 to 200 nm or from 10 to 100 nm. Thesilver alloy doping electrode 45 can be deposited utilizing any usefulmethod such as, for example, physical vapor deposition techniques. Inmany embodiments the silver alloy doping electrode 45 has planarized orsmooth surface, e.g., a surface RMS roughness of less than 2.0 nm.

FIG. 7 is a schematic diagram of an illustrative programmablemetallization memory cell 50 having a upper silver alloy dopingelectrode 55. The programmable metallization memory cell 50 includes afirst metal contact 56 and a second metal contact 54. The first metalcontact 56 is deposited on or adjacent to a semiconductor substrate 51,thus the first metal contact 56 can also be referred to as the lowermetal contact 56 or bottom metal contact 56. The second metal contact 54is deposited after the first metal contact 56. The second metal contact54 can also be referred to as the upper metal contact 54 or top metalcontact 54.

An ion conductor solid electrolyte material 52 (described above) isbetween the first metal contact 56 and the second metal contact 54. Asilver alloy doping electrode 55 separates the ion conductor solidelectrolyte material 52 from the second metal contact 54. The silveralloy doping electrode 55 includes an atomic mixture of silver atoms andaluminum atoms, copper atoms, gold atoms, ruthenium atoms, or titaniumatoms. In some embodiments the silver alloy doping electrode 55 includesan atomic mixture of silver atoms and aluminum atoms. In someembodiments the silver alloy doping electrode 55 includes an atomicmixture of silver atoms and copper atoms. In some embodiments the silveralloy doping electrode 55 includes an atomic mixture of silver atoms andtitanium atoms. The silver alloy can be formed of any useful amount ofsilver and other metal as described above. In many embodiments thesilver alloy includes from 50 to 85% atomic % sliver and from 50 to 15atomic % of aluminum atoms, copper atoms, gold atoms, ruthenium atoms,or titanium atoms. The silver alloy doping electrode 55 can have anyuseful thickness. In many embodiments the silver alloy doping electrode55 has a thickness in a range from 5 to 200 nm or from 10 to 100 nm. Thesilver alloy doping electrode 55 can be deposited utilizing any usefulmethod such as, for example, physical vapor deposition techniques. Inmany embodiments the silver alloy doping electrode 55 has planarized orsmooth surface, e.g., a surface RMS roughness of less than 2.0 nm.

FIG. 8 is a flow diagram of an illustrative method of forming aprogrammable metallization memory cell 100. The method includesdisposing an ion conductor solid electrolyte material between an firstmetal contact and a second metal contact at block 101. The methodincludes depositing a silver electrode between the ion conductor solidelectrolyte material and the first or second metal contact, the silverelectrode having a surface RMS roughness of less than 2.0 nm at block102. The silver doping electrode can be a silver alloy doping electrodeor a bi-layer structure including a metal seed layer and a silver layer.

The silver alloy doping electrode can be formed utilizing physical vapordeposition techniques such as co-sputtering. Two sputtering targets canbe utilized to form the silver alloy where one target is silver and theother target is another metal, as described above.

Thus, embodiments of the PROGRAMMABLE METALLIZATION MEMORY CELL WITHPLANARIZED SILVER ELECTRODE are disclosed. The implementations describedabove and other implementations are within the scope of the followingclaims. One skilled in the art will appreciate that the presentdisclosure can be practiced with embodiments other than those disclosed.The disclosed embodiments are presented for purposes of illustration andnot limitation, and the present invention is limited only by the claimsthat follow.

1. A programmable metallization memory cell comprising: a first metalcontact and a second metal contact; an ion conductor solid electrolytematerial between the first metal contact and the second metal contact;and a silver alloy doping electrode separating the ion conductor solidelectrolyte material from the first metal contact or the second metalcontact, the silver alloy doping electrode comprising an atomic mixtureof silver atoms and aluminum atoms, copper atoms, gold atoms, rutheniumatoms, or titanium atoms.
 2. A programmable metallization memory cellaccording to claim 1 wherein the silver alloy comprises silver atoms andcopper atoms.
 3. A programmable metallization memory cell according toclaim 1 wherein the silver alloy comprises silver atoms and aluminumatoms.
 4. A programmable metallization memory cell according to claim 1wherein the silver alloy comprises silver atoms and titanium atoms.
 5. Aprogrammable metallization memory cell according to claim 1 wherein thesilver alloy comprises from 50 to 85 atomic % silver atoms and from 50to 15 atomic % of aluminum atoms, copper atoms, gold atoms, rutheniumatoms, or titanium atoms.
 6. A programmable metallization memory cellaccording to claim 1 wherein the silver alloy doping electrode has asurface RMS roughness of less than 2.0 nm.
 7. A programmablemetallization memory cell comprising: a first metal contact and a secondmetal contact; an ion conductor solid electrolyte material between thefirst metal contact and the second metal contact; and a silver dopingelectrode separating the ion conductor solid electrolyte material fromthe first metal contact, the silver doping electrode comprising a silverlayer and a metal seed layer separating the silver layer from the firstmetal contact.
 8. A programmable metallization memory cell according toclaim 1 wherein the metal seed layer comprises titanium, aluminum, orruthenium.
 9. A programmable metallization memory cell according toclaim 1 wherein the metal seed layer comprises titanium.
 10. Aprogrammable metallization memory cell according to claim 1 wherein themetal seed layer has a thickness in a range from 0.5 to 5 nm.
 11. Aprogrammable metallization memory cell according to claim 1 wherein thesilver doping electrode has a surface RMS roughness of less than 2.0 nm.12. A programmable metallization memory cell according to claim 1further comprising a semiconductor substrate, the silver electrode beingdisposed closer to the semiconductor substrate than the ion conductorsolid electrolyte material.
 13. A method of forming a programmablemetallization memory cell (PMC), comprising steps of: disposing an ionconductor solid electrolyte material between a first metal contact and asecond metal contact; depositing a silver doping electrode between theion conductor solid electrolyte material and the first metal contact orsecond metal contact, the depositing step forming a silver dopingelectrode having a surface RMS roughness of less than 2.0 nm.
 14. Amethod of forming a programmable metallization memory cell according toclaim 13, wherein the depositing step comprises depositing a silverdoping electrode comprising an atomic mixture of silver atoms andaluminum atoms, copper atoms, gold atoms, ruthenium atoms, or titaniumatoms.
 15. A method of forming a programmable metallization memory cellaccording to claim 13, wherein the depositing step comprises depositinga metal seed layer and depositing a silver layer on the metal seedlayer, the metal seed layer separating the silver layer from the firstmetal contact.
 16. A method of forming a programmable metallizationmemory cell according to claim 13, wherein the depositing step comprisesdepositing the silver doping electrode closer to a semiconductorsubstrate than the ion conductor solid electrolyte.
 17. A method offorming a programmable metallization memory cell according to claim 15,wherein the depositing step comprises depositing the metal seed layercloser to a semiconductor substrate than the silver layer.
 18. A methodof forming a programmable metallization memory cell according to claim15, wherein the metal seed layer comprises titanium and the metal seedlayer has a thickness of less than 5 nm.
 19. A method of forming aprogrammable metallization memory cell according to claim 13, whereinthe depositing step is provided by a physical vapor depositiontechnique.
 20. A method of forming a programmable metallization memorycell according to claim 15, wherein the disposing step comprisesdepositing the ion conductor solid electrolyte material on the silverdoping electrode.